The invention relates to a method of heat treatment of a length of material in a tentering machine, particularly for drying, fixing and/or condensing.
It has been usual in the past to regulate a tentering machine on the so-called feed-back principle, which will be explained using the example of regulating the temperature by means of an air heater. A temperature sensor is located behind the air heater and passes its measured value to a regulator which compares the measured value with a preset theoretical value. The difference between these two values results in a control value which acts on a control member, which in the hypothetical case discussed here can for example be a regulating valve which alters the quantity of flow on the fluid side of the air heater. This feedback coupling closes the control circuit. The air temperature must be altered before the measuring and control circuit can emit a new setting signal.
The application of this conventional feed-back regulation to the operation of a tentering machine has the disadvantage that particularly before the commencement of heat treatment the plant is not yet at an optimum setting, which leads to uneconomic operation with unnecessarily high energy costs and in certain circumstances impairs the quality of the material.